Electrical protective relays



March 14, 1967 P. MORETON ELECTRICAL PROTECTIVE RELAYS Filed Sept. 9,1963 FIG.1

.rzmdd DU adssmom FORWARD VOLTS United States Patent 0 3,309,582ELECTRICAL PROTECTIVE RELAYS Peter Lewis Moreton, Feiton, Somerset,England, assignor to The English Electric Company Limited, London,England, a British company Filed Sept. 9, 1963, Ser. No. 307,422 Claimspriority, application Great Briafin, Sept. 11, 1962, 34,737/ 62 4Claims. (Cl. 317-123) The invention relates to electrical protectiverelays, that is to say, to relays operative under predeterminedconditions to perform a protective function for, for example, bringingabout automatic de-energisation and/or disconnection of electrical plantfrom its source of supply.

According to the invention, an electrical time-overcurrent protectiverelay includes a relay operating element for energisation by anoperating current supplied thereto for performing in response to suchoperating current a protective function after a time delay dependentupon the magnitude of the operating current, and a relay input circuitarrangement having first and second input terminals for connection witha source of unidirectional cur rent which is to be monitored by therelay, first and second output terminals connected with the relayoperating element for transmitting thereto the said operating current,shunt electric circuit means connected between the first and secondinput terminals and including in series with one another a non-linearresistor and an adjustable linear resistor (hereafter referred to as thefirst adjustable able linear resistor), the said non-linear resistorexhibiting alternatively a high resistance value or a low resistancevalue according to whether a unidirectional current carried thereby liesin a predetermined range of low values or in a predetermined range ofhigher values respectively, and these resistance values being such thatfor a predetermined range of low input current values the non-linearresistor exhibits its high resistance value and prevents adjustment ofthe first adjustable linear resistor having any substantial influence onthe ratio operating current/input current, adjustment of this ratio tocalibrate the relay time delay at a predetermined first input currentvalue, lying in the said range of input current values, being obtainableby way of adjustment of the second adjustable linear resistor only, andsuch that for a predetermined range of higher input current values thenon-linear resistor exhibits its low resistance value and enablesadjustment of the first adjustable linear resistor to be effective toprovide adjustment of the said ratio whereby to calibrate the relay timedelay at a predetermined second input current value, lying Within thesaid predetermined range of higher'input current values, withoutsubstantially upsetting the calibration of the relay time delay at thesaid predetermined first input current value as determined by thesetting of the second adjustable linear resistor.

Such an electrical time-over current relay may also include at least oneother relay input circuit arrangement similar to the aforesaid relayinput circuit arrangement, each such other relay input circuitarrangement having Patented Mar. 14, 1967 its first and second outputterminals connected to the first. and second input terminalsrespectively of the succeeding relay input circuit arrangement, and theresistance 7 values of the non-linear resistor of each such other relayinput circuit arrangement being such that calibration of the relay timedelay at a predetermined lower input current value which is greater thanthe predetermined greater input current value in respect of thesucceeding relay input circuit arrangement is obtainable by adjustmentof the second adjustable linear resistor of the relay input circuitarrangement without upsetting the calibration of the relay time delay asdetermined by the settings of the first and second adjustable linearresistors of any succeeding relay input circuit arrangement, thenon-linear resistor of the relay input circuit arrangement thenexhibiting its high resistance value, and such that calibration of therelay time delay at a predetermined greater input current value isobtainable by adjustment of the first adjustable linear resistor of therelay input circuit arrangement without substantially upsetting thecalibra tion of the relay time delay as determined by the setting of thesecond adjustable linear resistor of the relay input circuitarrangement, the non-linear resistor of the relay input circuitarrangement then exhibiting its low resistance value.

Preferably, the or each non-linear resistor means comprises one or morediodes.

An electrical time-overcurrent protective relay embodying the inventionwill now be described by way of example and with reference to theaccompanying drawing in which:

FIG. 1 is a diagram of the circuit of the relay; and

FIG. 2 is a characteristic curve of a typical non-linear resistancedevice for use in the circuit of FIG. 1.

Referring toFIG. l, the winding 10 of the relay rotor (not shown) isconnected, through control spring ligaments 11 and through a two stageinput circuit 12, to relay input terminals 13 connected to the circuitto be protected by the relay. The connection is made via currenttransforming and rectifying means (not shown) so that the relay issupplied with a direct current represent ing the magnitude of thealternating current in the protected circuit. The rotor is arranged toco-operate with the poles of a stationary magnet (not shown) so that atorque acting to rotate the rotor is produced when the rotor windingcarries a current.

The input circuit 12 consists of two stages, one stage comprising aseries resistor 14 and ashunt circuit 16 and the other stage comprisinga series resistor 15 and a shunt circuit 17.

The shunt circuit 16, which is connected across the ter minals 13,consists of a series arrangement of a resistor 18 and two diodes 19, 20. The shunt path 17, one end of which is connected to the junction ofthe resistors 14 and 15, consists of a resistor 21 in serieswith a diode22. The resistors 14, 15, 18 and 21 are all linear resistors and are alladjustable. I

The input circuit 12 has the effect of causing an increasing proportionof the input current from the terminals 13 to by-pass the rotor winding10 as this input current increases. This has the effect of modifying thenormal very inverse time-overcurrent characteristic of the relay (bywhich is meant a characteristic such that the operating time of therelay is inversely proportional to a the operating current) to produce aless inverse char-' acteristic.

The proportion of input current to the relay from the terminals 13 whichis by-passed through the shunt paths 16, 17 depends on the relativeresistances of the winding 10, the variable resistors 14, 15, 18, and 21and the slope resistance of the diodes 1?, 2t 22. The slope resistanceof the diodes depends on the current flowing through them, that is, onthe magnitude of the input current, because of their non-linearresistance-current characteristic. The parameters of the circuit are sochosen that, with a relay input current of twice the pick-up current ofthe relay (that is, twice the current required to initiate movement ofthe rotor), the shunt path 17 is slightly conductive whilst the shuntpath 16 is nonconductive.

Referring now to FIG. 2, at twice the pick-up current of the relay, thediode 22 operates at a point on its characteristic corresponding to thevoltage b. The voltage across the diode 22 can be varied between thepoints a and c on the characteristic shown in FIG. 2 by adjustment ofthe resistor 15, so that a corresponding change can be made in theproportion of input current bypassing the rotor winding 10. Thisadjustment alters the operating time of the relay for a relay inputcurrent of twice the pick-up value and thus provides a means ofcalibration at that value of relay input current.

It the input current rises to five times the pick-up current of therelay, the point of operation of the diode 22 is moved to the point onits characteristic corresponding to the voltage at, that is, the diodebecomes more conductive. At this level of input current, the other shuntpath 16 is however still non-conductive.

At this point of operation of the diode 22, its slope resistance is onlya fraction of an ohm. Therefore, adjustment of the resistor 21 has anappreciable efiect on the proportion of input current which is by-passedthrough the shunt path 17 and hence provides adjustment of the operatingtime of the relay for a relay input current of five times the pick-upvalue, and hence a means of calibration at that value of relay inputcurrent. However, any adjustment of the resistor 21 for the purpose ofcalibrating the relay at five times the pick-up current has very littledisturbing effect on the calibration of the relay operating time attwice the pick-up current obtained by adjustment of resistor 15 asdescribed above, because the slope. resistance of the diode 22 is muchhigher at twice the pickup current than at five times the pick-upcurrent. In other words, the proportion of input current fiowing throughthe resistor 21 is very much lower at tiwce the pick-up current than itis at five times the pick-up current, and therefore any adjustment ofresistor 21 will have little ettect on the proportion of input currentflowing through the rotor winding 19 at twice the pick-up current.

The calibration of the relay operating time at ten times the pick-upcurrent is obtained by suitable adjustment of the resistor 14, thediodes 19 and 20 then being of high resistance, and the calibration attwenty times the pick-up current is obtained by adjustment of theresistor 18, the diodes 19 and 29 then being of low resistance. Thevariation in slope resistance of the diodes 19 and 20 ensures that theseadjustments will not substantially affect the other calibrationsobtained by adjustment of the resistors 15 and 21. Thus any deviation ofthe time-overcurrent characteristic of the relay from the desired shape,which deviation may for example be due to departure of the diode and/ orrotor winding resistances from their nominal values, may be corrected.

It is not necessary to provide means for compensating for ambienttemperature variation because the diodes 19, 20 and 22 are so chosenthat their temperature coefficients of resistance are matched to that ofthe rotor winding so as to render the relay self-compensating forchanges in ambient temperature.

What I claim as my invention and desire to secure by Letters Patent is:

1. An electrical time-overcurrent protective relay including a relayoperating element for energisation by an operating current suppliedthereto for performing in response to such operating current aprotective function after a time delay dependent upon the magnitude ofthe operating current, and a relay input circuit arrangement havingfirst and second input terminals for connection with a source ofunidirectional current which is to be monitored by the relay, first andsecond output terminals connected with the relay operating element fortransmitting thereto the said operating current, shunt electric circuitmeans connected between the first and second input terminals andincluding in series with one another a nonlinear resistor and anadjustable linear resistor (hereafter referred to as the firstadjustable linear resistor), serial electric circuit means includingfirst electric circuit means connected between the first input terminaland the first output terminal, and second electric circuit meansconnected between the second'input terminal and the second outputterminal, one of the said first and second electric circuit meansincluding an adjustable linear resistor (hereafter referred to as thesecond adjustable linear re sistor), the said non-linear resistorexhibiting alternatively a high resistance value or a low resistancevalue according to whether a unidirectional current carried thereby liesin a predetermined range of low values or in a predetermined range ofhigher values respectively, and these resistance values being such thatfor a predetermined range of low input current values the non-linearresistor exhibits its high resistance value and prevents adjustment ofthe first adjustable linear resistor having any substantial influence onthe ratio operating current/input current, adjustment of this ratio tocalibrate the relay time delay at a predetermined first input currentvalue, lying in the said range of input current values, being obtainableby way of adjustment of the second adjustable linear resistor only, andsuch that for a predetermined range of higher input current values thenon-linear resistor exhibits its low resistance value and enablesadjustment of the first adjust able linear resistor to be effective toprovide adjustment of the said ratio whereby to calibrate the relay timedelay at a predetermined second input current value, lying within thesaid predetermined range of higher input current values, withoutsubstantially upsetting the calibration of the relay time delay at thesaid predetermined first input current value as determined by thesetting of the second adjustable linear resistor.

2. An electrical time-overcurrent protective relay according to claim 1,including at least one other relay input circuit arrangement similar tothe aforesaid relay input circuit arrangement, each such other relayinput circuit arrangement having its first and second output terminalsconnected to the first and second input terminals respectively of thesucceeding relay input circuit arrangement, and the resistance values ofthe non-linear resistor of each such other relay input circuitarrangement being such that calibration of the relay time delay at apredetermined lower input current value which is greater than thepredetermined greater input current value in respect of the succeedingrelay input circuit arrangement is ob tainable by adjustment of thesecond adjustable linear resistor of the relay input circuit arrangementwithout upsetting the calibration of the relay time delay as determinedby the settings of the first and second adjustable linear resistors ofany succeeding relay input circuit arrangement, the non-linear resistorof the relay input circuit arrangement then exhibiting its highresistancevalue, and such that calibration of the relay time delay at apredetermined greater input current value is obtainable by adjustment ofthe first adjustable linear resistor of the relay input circuitarrangement without substantially upsetting the calibration of the relaytime delay as determined by the setting of the second adjustable linearresistor of the relay input circuit arrangement, the non- 5 6 linearresistor of the relay input circuit arrangement then References Cited bythe Examiner l is e l e ct c al t rrifa ij rfi r r ent protect've relayac UNITED STATES PATENTS n 1 I e l 1 cording to claim 1, wherein thenon-linear resistor com- 1200,796 10/1916 Arnold 31720 X prises a diodedevice 5 2,28 ,423 5/ 1942 Hansell 317-41-X 4. An electricaltime-overcurrent urotective relay aci 1 I F cording tociaim 2, whereineach non-linear resistor COID- M LTON O HIRSHFICLD 1mm y Exawme' prisesa diode device. I. D. TRAMMELL, Assistant Examiner.

1. AN ELECTRICAL TIME-OVERCURRENT PROTECTIVE RELAY INCLUDING A RELAYOPERATING ELEMENT FOR ENERGISATION BY AN OPERATING CURRENT SUPPLIEDTHERTO FOR PERFORMING IN RESPONSE TO SUCH OPERATING CURRENT A PROTECTIVEFUNCTION AFTER A TIME DELAY DEPENDENT UPON THE MAGNITUDE OF THEOPERATING CURRENT, AND A RELAY INPUT CIRCUIT ARRANGEMENT HAVING FIRSTAND SECOND INPUT TERMINALS FOR CONNECTION WITH A SOURCE OFUNIDIRECTIONAL CURRENT WHICH IS TO BE MONITORED BY THE RELAY, FIRST ANDSECOND OUTPUT TERMINALS CONNECTED WITH THE RELAY OPERATING ELEMENT FORTRANSMITTING THERETO THE SAID OPERATING CURRENT, SHUNT ELECTRIC CIRCUITMEANS CONNECTED BETWEEN THE FIRST AND SECOND INPUT TERMINALS ANDINCLUDING IN SERIES WITH ONE ANOTHER A NONLINEAR RESISTOR AND ANADJUSTABLE LINEAR RESITOR (HEREAFTER REFERRED TO AS THE FIRST ADJUSTABLELINEAR REISTOR (HERESERIAL ELECTRIC CIRCUIT MEANS INCLUDING FIRSTELECTRIC CIRCUIT MEANS CONNECTED BETWEEN THE FIRST INPUT TERMINAL ANDTHE FIRST OUTPUT TERMINAL, AND SECOND ELECTRIC CIRCUIT MEANS CONNECTEDBETWEEN THE SECOND INPUT TERMINAL AND THE SECOND OUTPUT TERMINAL, ONE OFTHE SAID FIRST AND SECOND ELECTRIC CIRCUIT MEANS INCLUDING AN ADJUSTABLELINEAR RESISTOR (HEREAFTER REFERRED TO AS THE SECOND ADJUSTABLE LINEARRESISTOR), THE SAID NON-LINEAR RESISTOR EXHIBITING ALTERNATIVELY A HIGHRESISTANCE VALUE OR A LOW RESISTANCE VALUE ACCORDING TO WHETHER AUNIDIRECTIONAL CURRENT CARRIED THEREBY LIES IN A PREDETERMINED RANGE OFLOW VALUES OR IN A PREDETERMINED RANGE OF HIGHER VALUES RESPECTIVELY,AND THEESE RESISTANCE VALUES BEING SUCH THAT FOR A PREDETERMINED RANGEOF LOW INPUT CURRENT VALUES THE NON-LINEAR RESISTOR EXHIBITS ITS HIGHRESISTANCE VALUE AND PREVENTS ADJUSTMENT OF THE FIRST ADJUSTABLE LINEARRESISTOR HAVING ANY SUBSTANTIAL INFLUENCE ON THE RATIO ''OPERATINGCURRENT/INPUT CURRENT'', ADJUSTMENT OF THIS RATIO TO CALIBRATE THERELAWY TIME DELAY AT A PREDETERMINED FIRST INPUT CURRENT VALUE, LYING INTHE SAID RANGE OF INPUT CURRENT VALUES, BEING OBTAINABLE BY WAY OFADJUSTMENT OF THE SECOND ADJUSTABLE LINEAR RESISTOR ONLY, AND SUCH THATFOR A PREDETERMINED RANGE OF HIGHER INPUT CURRENT VALUES THE NON-LINEARRESISTOR EXHIBITS ITS LOW RESISTANCE VALUE AND ENABLES ADJUSTMENT OF THEFIRST ADJUSTABLE LINEAR RESISTOR TO BE EFFECTIVE TO PROVIDE ADJUSTMENTOF THE SAID RATIO WHEREBY TO CALIBRATE THE RELAY TIME DELAY AT APREDETERMINED SECOND INPUT CURRENT VALUE, LYING WITHIN THE SAIDPREDETERMINED RANGE OF HIGHER INPUT CURRENT VALUES, WITHOUTSUBSTANTIALLY UPSETTING THE CALIBRATION OF THE RELAY TIME DELAY AT THESAID PREDETERMINED FIRST INPUT CURRENT VALUE AS DETERMINED BY THESETTING OF THE SECOND ADJUSTABLE LINEAR RESISTOR.